Many large circulation periodicals and great numbers of mail order catalogs and large distribution advertising pieces consist of signatures, often with return card inserts, which are gathered on an inserter for saddle stitching, trimming, bundling for minimum shipping costs, and shipping. For present purposes all such publications can be referred to as "saddle stitched books".
The high volume of saddle stitched books presently produced by the U.S. printing industry requires that the most efficient possible use be made of manpower, equipment and plant space. A typical inserter has 32 packer boxes, each of which receives signatures seriatim from a signature supply means, opens each signature, and drops the signatures successively straddling a gathering chain that runs in front of the packer boxes and carries the complete collections of gathered signatures to the saddle stitcher.
The need for highly efficient plant operations results in a constant effort to increase the speed at which inserters and saddle stitchers operate, and their reliability so as to minimize shutdowns due to malfunctions. It is obvious that as machines operate at higher and higher cyclic rates the possibility of malfunctions increases.
Demands for increased plant efficiency are pushing the cyclic rate of bindery lines up from the vicinity of 150 books a minute to a present target figure of about 300 books a minute. Such an enormous increase in the speed of operation necessarily requires the development of new techniques for handling the signatures at all stages of the binding process. High speed operation of packer boxes and a gathering chain presents some particularly difficult problems produced by the need for the inserter to handle signatures that may vary from four pages to 32 pages, and that may consist of a variety of different paper stocks that have varying handling and feeding characteristics. The very high speed handling of paper presents problems that are unknown at lower speeds.
An advance in the rate of bindery operation is illustrated by a comparison between Kleineberg Pat. No. 2,413,358 and McCain Pat. No. 3,565,422. In Kleineberg an extracting drum has two sets of signature grippers and a transfer drum and opener drum each have one set of grippers. In McCain the extracting drum has three sets of grippers and the transfer drum and the opener drum each have two sets. Obviously if the McCain transfer drum and opener drum are driven at the same RPM as those of Kleineberg, the inserter feeds twice as many signatures per minute to the gathering chain.
The basic operation of an inserter has not changed from that disclosed in Pat. No. 2,413,358. An extracting drum has a movable jaw that receives the closed end of a signature and the rotation of the extracting drum carries the signature around to a point where its closed end abuts a register stop and its open end is opposite grippers on a transfer drum. The extracting drum jaws open, the transfer drum grippers close on the open end of the signature and rotation of the transfer drum strips the signature from the extracting drum. Standard practice in saddle stitching requires the use of lap signatures--i.e. those in which one sheet of the signature (the lap sheet) is wider than is the other sheet of the signature.
The gripper means on the transfer drum initially grip both the lap sheet and the short sheet, and when the gripped signature margins are confronting an opener drum the short sheet is released while the lap sheet remains gripped, whereupon the short sheet is gripped by a clamp on the opener drum so that the continuing rotation of the transfer drum and the opener drum spreads the signature to drop it straddling the gathering chain.
It is quite apparent that as the rotational speeds of the three drums increase, the behavior of the free edges of the signatures on the extracting drum also changes. A persistent problem in high speed operation of an inserter is that of controlling the trailing open end portion of the signature so that it is properly gripped by the grippers of the transfer drum. Increased rotational speed of the extracting drum increases the centrifugal force tending to swing the trailing end of the signature away from the drum, and it also greatly changes air turbulence effects that result from proximity of the drum surface to a concentric guide shoe and also from the irregularities in the drum surface produced by the jaw clamps, register stops, and malfeed detectors.
Overall plant efficiency can be increased both by higher cyclic rates of operation and by reducing the time required to make any necessary changes or adjustments in the apparatus to go from one job to the next or to switch from one type of signature supply means to another. Comparison of FIG. 1 of Swanson Pat. No. 3,880,419 with FIG. 2 of McCain Pat. No. 3,565,422 shows that the extracting drum receives signatures from the feed hopper at a totally different point in its rotation from that at which it receives signatures from a stream feeder.